The filesystem used in the vast majority of Linux (and to a lesser extent on other Unix) distributions is the ext3 filesystem, which stands for extended filesystem. Slashdot recently pointed to an article on IBM DeveloperWorks discussing the new ext4 filesystem currently in development, and some of its new features. So what is a filesystem really? And why is the development of ext4 and the new features it brings to the table important for open source platforms?